The invention relates to an energy storage system for supplying electric energy to consuming devices in a vehicle, particularly in a motor vehicle, as well as to a method of regenerating an energy accumulator in such an energy storage system.
It is known to use two mutually coupled power grids with corresponding energy accumulators for each energy system for supplying electric energy to consuming devices in modern vehicles and, particularly, in automobiles. European Patent document EP 1 130 737 B1, for example, describes an electric energy supply system having a low direct-current grid and a high direct-current grid, which are mutually coupled by way of a DC-DC converter. In this case, the energy accumulators of the two grids are connected in series.
The energy accumulators of an energy storage system integrated in a vehicle and consisting of at least two energy accumulators are cyclically discharged and charged during the operation. Over a longer period of time, this leads to a deterioration of the performance of the energy accumulator or to a shortening of the useful life of the energy accumulators. Methods are therefore known from the state of the art by which an energy accumulator in an energy storage system can be regenerated in a suitable manner in order to thereby counteract the deterioration of the functionality of the energy accumulator or the shortening of its useful life.
International Patent document WO 2007/104325 A1 discloses a method of regenerating a capacitive energy accumulator in the form of a cell composite of series-connected cells consisting of double-layer capacitors. These types of energy accumulators are frequently also called supercaps and permit the accumulation of energy of a high power density. Here, it is problematic that, as a result of the cyclical charging and discharging of the cell composite, voltage drifts will occur between the individual cells which, in some cells, result in excess voltages and, in other cells, result in insufficient voltages. The regeneration described in International Patent document WO 2007/104325 A1 is based on a charging operation, which carries out a balancing of circuits of the cells, so that, by means of all cells, the same voltage is generated again. In this case, a so-called active bypass balancer circuit is used which, during the implementation of the balancing of circuits, ensures that when an excess voltage is too high in a cell, current is discharged by way of an electric resistor.
The methods known from the state of the art for regenerating an energy accumulator in an energy storage system of a vehicle have the disadvantage that impairments of the functionalities of the vehicle may occur when implementing the regeneration, particularly if the regeneration operation is started during the travel of the vehicle.
It is therefore an object of the invention to ensure in an energy storage system of a vehicle consisting of two energy accumulators that the operation of regenerating an energy accumulator is carried out without, or only with a slight, impairment of functionalities of the vehicle.
This and other objects are achieved by an energy storage system and method for supplying electric energy to consuming devices in a vehicle, particularly in a motor vehicle, comprising a first power grid having a first energy accumulator and a second power grid having a second energy accumulator. The first and the second power grid are electrically coupled such that electric energy from the first power grid can be fed to the second power grid for regenerating the second energy accumulator. The energy storage system can be operated such that it detects when a number of conditions has been met, the number of conditions comprising at least the condition that an external charging device is connected to the first power grid for charging the first energy accumulator. In the event that the number of conditions has been met, the regenerating of the second energy accumulator is carried out.
The energy storage system according to the invention comprises a first power grid having a first energy accumulator and a second power grid having a second energy accumulator, the first and the second power grid being electrically coupled—for example, by way of a converter or switch—such that electric energy from the first power grid can be fed to the second power grids for regenerating the second energy accumulator. The first power grid and second power grid preferably are direct-current grids which are mutually coupled by way of a DC-DC converter. The first and the second energy accumulator of the two power grids may be mutually connected in parallel or, if required, in series.
The energy storage system is characterized in that it can be operated such that it is detected when a number of conditions has been met, the number of conditions comprising at least the condition that an external charging device, which is not part of the energy storage system, is connected to the first power grid for charging the first energy accumulator. If the number of conditions has been met, the regeneration of the second energy accumulator will be carried out.
The invention is based on the recognition that, when a regeneration of an energy accumulator is carried out, the system functionalities of the vehicle, as a rule, will be impaired the least if the charging operation is carried out by an external charging device. The reason is that, when an external charging device is connected, usually no further functionalities or electrical consuming devices of the vehicle are used and the operation of the vehicle is therefore not impaired.
In a particularly preferred embodiment of the energy storage system according to the invention, the number of conditions, in addition to the above condition that an external charging device is connected, may comprise one or more additional conditions which can be used, for example, for making it plausible that no additional consuming devices are used which are fed by the energy storage system. In particular, the number of conditions may further comprise the condition or conditions that the vehicle is stationary, the ignition of the vehicle is switched off, and/or no condition is detected that deviates from the normal state of the second energy accumulator. The last-mentioned condition has the purpose of ensuring that no faulty operating condition of the energy accumulator is present when the regeneration is carried out, which faulty operating condition, under certain circumstances, may lead to damage to the energy accumulator. Such a condition, which deviates from the normal state of the energy accumulator, may, for example, be detected by measuring the temperature of the second energy accumulator, in which case it is determined that a condition is present that deviates from the normal state if the temperature exceeds a predetermined threshold value. In this case, the regeneration of the second energy accumulator will not be initiated.
Analogous to the above conditions, whose fulfillment starts the regenerating function for the second energy accumulator, corresponding termination conditions are also provided in a particularly preferred embodiment of the invention, in the event of whose fulfillment, the regeneration of the second energy accumulator is stopped. When carrying out the regeneration of the second energy accumulator, it is checked in this case whether at least one termination condition out of a number of termination conditions has been met.
In a variant of the invention, the termination conditions are further developed such that a termination condition will have been met if at least one of the above conditions, according to which the regeneration was started, has not been met. In particular, the number of termination conditions may comprise one or more of the following termination conditions:
(a) the external charging device is terminated by the first power grid;
(b) the ignition of the vehicle is switched on; and/or
(c) a condition is detected that deviates from the normal state of the second energy accumulator.
In a further development of the energy storage system according to the invention, the regeneration of the second energy accumulator will be terminated after it was carried out successfully. As required, the regenerating may also still be continued for a predetermined time period, particularly until a predefined state of charge of the first energy accumulator has been reached, for example, until the first energy accumulator is fully charged.
In a further development of the method according to the invention, the regeneration is based on the initially mentioned balancing of circuits of the second energy accumulator, in which case any arbitrary balancing method can be used that is known from the state of the art. In particular, the balancing of circuits takes place by an active bypass circuit in the second power grid, which was described initially. The balancing of circuits is preferably carried out based on the method described in International Patent document WO 2007/104325 A1.
In a particularly preferred embodiment of the energy storage system according to the invention, the first energy accumulator of the first power grid is a battery, particularly a 12V battery, for example, a lead battery or a nickel metal hydride battery. In this case, the first power grid preferably is the conventional on-board power system of a vehicle, by way of which the majority of the electric consuming devices of the vehicle are fed.
In a further development of the method according to the invention, the second energy capacitor of the second power grid is a capacitive energy accumulator, particularly the above-mentioned energy accumulator consisting of one or more cells of double-layer capacitors. In this case, the second power grid preferably is an expansion of the conventional on-board power supply system of the vehicle, which is used for feeding consuming devices which require a voltage deviating from the on-board power supply system or which consume a large amount of power in certain configurations and, for this purpose, require the aid of a second energy accumulator.
In a further development of the method according to the invention, the second power grid is the power grid of the electric motor of a hybrid drive which has a second energy accumulator for driving the electric motor. Since it can be assumed that the hybrid drive is not in operation when an external charging device is connected, the system functionalities of this drive are not limited thereby when the regeneration is carried out.
In addition to the above-described energy storage system, the invention relates to a method of regenerating an energy accumulator in such an energy storage system, the method being usable in combination with each variant of the above-described energy storage system. The method is thereby used in an energy storage system which comprises a first power grid having a first energy accumulator and a second power grid having a second energy accumulator, the first and second power grid being electrically coupled such that electric energy from the first power grid can be fed to the second power grid for regenerating the second energy accumulator. In this case, it is detected when a number of conditions has been met, the number of conditions comprising at least the condition that an external charging device is connected to the first power grid for charging a first energy accumulator. If required, the conditions may also comprise further conditions that were described above. In the event that the number of conditions has been met, the regenerating of the second energy accumulator is carried out, the regenerating especially being the above-described balancing of circuits. In this case, the method is preferably applied in energy storage systems in which the second energy accumulator is a capacitive energy accumulator, particularly a cell composite consisting of one or more cells of double-layer capacitors.
In addition to the above-described energy storage system and method, the invention also relates to a vehicle, particularly a motor vehicle, that includes the energy storage system according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.